3.5.2 PCIe AXI Slave IF Throughput

Throughput calculation is carried out at 250 MHz AXI CLK using fabric AXI DMA (64 KB of DMA size), maximum payload of 128 Bytes. The fabric AXI DMA 256-beat AXI burst length transactions on AXI slave IF. When using AXI slave IF, four PCIe outstanding transactions are supported.

Table 3-10. PCIe AXI Slave IF Throughput
Link WidthLink SpeedPC to LSRAM (Memory Read from PC)LSRAM to PC (Memory Write 
to PC)Maximum Theoretical Throughput (MBps)
Maximum Throughput (MBps)% of Theoretical ThroughputThroughput (MBps)% of Theoretical Throughput
x1Gen120481.622690.4250
Gen241182.245390.6500
x2Gen139779.444088500
Gen259959.987787.71000
x4Gen148348.383183.11000
Gen266533.25164682.32000

PCIe Throughput depends on the following factors:

  • PCIe uses 8b10b encoding, which causes 20% reductions in throughput.
  • The maximum PCIe read throughput also depends on the supported PCIe outstanding transactions and Round-trip time (RTT).
  • Maximum effective bandwidth is the rate at which valuable data is transferred at a particular point. It does not include transaction overhead, such as headers, sequence numbers, CRCs, ECRCs, and other packets like DLLPs and SKIP advanced sets.
 Maximum Effective Bandwidth = data/(data + overhead)

The following table lists the relation between maximum transaction payload size and efficiency. Increasing the transaction payload size (increasing the burst length) also improves throughput.

Table 3-11. Relation Between Maximum Transaction Payload Size and Efficiency
Maximum Transaction Payload Size (Byte)Efficiency
12886%
25692%